Palaeoglaciology 1: landsystems Flashcards
What is the inversion concept?
the idea that using landforms to reconstruct the characteristics of the past ice sheet can also be inverted to use the knowledge of ice sheets today to know how landforms were created previously
What are landsystems?
common terrains attributes of topography, soils and vegetation that reflect an underlying geology, past erosional and depositional processes and climate
What are the components of a landsystem?
Elements = individual landforms Units = groups of elements Landsystems = recurrent patterns between different units
What is a glacier surge?
A multi-year oscillation between extended periods of normal motion and brief periods of comparatively fast motion (Raymond, 1987)
Why do surges happen?
An excess of accumulation above that which normal flow cannot discharge thereby causing it to increase which is known as a ‘surge’
What are the two phases/states of surge glaciers?
Active = rapid (10-100x faster) flow that can last as little as 1-5 years occurring every 10-200 years Quiescent = slow motion between the active phases
What are the two hypothesised triggers for a glacier surge?
1) collapse of drainage tunnels releases trapped water leading to building up of pressure that releases meltwater supply to bed that causes detachment and sliding
2) Water drainage through permeable subglacial sediment, permeability reduces ice thickness which causes the ice pressure to accumulate and then initiates rapid motion
How many characteristic landform types do terrestrial landsystems have? Who said this?
8 - Evans et al. 1999
What are the 8 landform types divided in to?
4 formed during active phase
4 formed during quiescent phase
What are flutes?
small-scale linear features
How do flutes form?
when the glacier surges it will have a boulder embedded in its base that deforms resulting in a flute of sediment within a cavity as it moves forward.
What are overridden moraines and how are they formed?
during the surge over a foreland, pre-existing moraine ridges formed by previous surges are overridden by the glacier which creates a domed hill over the top.
What are the overridden moraines covered with?
A carapace of subglacial till that it smoothed out into fluted mounds
What are glaciotectonic composite ridges?
Sediment wedges that form during a glacier surge and then pile on top of each other during successive surges
How do glaciotectonic composite ridges form?
During advance at the termination of the surge the glacier surge thrusts proglacial sediments in to ridges that solidify as wedges
What are blowout structures and how do they form?
As a result of the build up of subglacial meltwater before a surge, when it surges the meltwater can be ejected violently through a blow out that can also create a hole in the landscape.
What are hummocky moraines and how are they formed?
During the active phase a lot of water and sediment accumulate at the snout of the glacier. At the end of this phase ice blocks melt out and can be left at the ice-marginal position. Eventually the ice will melt leaving debris to melt out the ice
How are outwash tracks formed and what are they?
At the end of surge phase and through following quiescent phase, proglacial outwash occurs and small proglacial lakes form at the snout. Glaciofluvial sediment is then deposited here at the end of the phase. The channels and lakes infill outwash tracks of stagnant ice blocks with sediment
What are concertina eskers?
Zig-zaged eskers
How do concertina eskers form?
When an englacial or subglacial channel that carries both water and sediment deposits it material and the ice melts away. The zig zag shape derives from how the channels were forced to find the path of least resistance when they were active which involves joining up lots of small englacial channels and the since deformation that has occurred to the glacier
What are crevasse squeeze ridges and how do they form?
During a surge sediment will be forced upwards in to crevasses within the ice. when the ice then retreats it needs to do so slowly so that these ridges are then preserved
